in the first level (after training level)when you man the browing 50.cal once you get to the broken down convoy,a black hawk will fly over,shoot the heak out of it.it will then blow into pieces,BUT!!you will start over.Oh and when get to the broken down convoy stay in and wait for the black hawk to fly over. p.s.in another level (the swamp)when you land set afew satchel charges in the chopper get out,set them off when it flys away,set them off,may have to use at4
On the mission Lost Convoy at the end when you have to help the survivors of black hawk by sniping the rpg militia, go to the barrels to the right of the ammo and health packs and jump. You will have easier access to shooting up there.